Tone control



June 21, 1949.

Filed June 6, 1947 J D- REID ETAL ToNE-coNTRoL 2 Sheets-Sheet 1 June 21, 1949. 1 D, REID ET AL 2,474,191

TONE CONTROL Filed June 6, 1947 k 2 sheets-,sheet 2 680mm; Geom/,cp JZaIcWMf-zzz -4 37 ff IV 44 I 32 f 3@ f4 Patented June 271, 1949 UNITED STATES OFFICE TONE CONTROL Application June 6, 1947, Serial No. 752,878

5 Claims.

This invention relates to a method and apparatus for tone control of electric sound reproducing systems such as are found in radio receivers and phonographs.

In tone control apparatus heretofore employed for differentiating the amplification of the upper and lower registers of sound it has been common practice to first adjust either the treble or bass register and then adjust the entire volume level of output. It has thus been necessary to utilize several operations before satisfactory adjustment is obtained. This process has been necessarily commonly employed each time a diiferent tone adjustment is desired.

An object of this invention is to provide a novel tone control by means of which either the upper and lower registers may be accentuated or suppressed without the necessity of altering the general volume level.

Another object of this invention is to provide a tone `control mechanism by which the upper register may be suppressed and the lower register simultaneously accentuated.

A further object of this invention is to provide a tone control mechanism by which the upper register may be accentuated and the lower register simultaneously suppressed.

A still further object of this invention is to provide a tone control system consisting of dual channel circuits having mechanically intercon- A nected Volume controls in each circuit and speakers independently associated with each of said circuits.

The novel features that we consider characteristie of our invention are set forth in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description thereof when read in conjunction with the accompanying drawing, in which:

Fig. l is a schematic diagram in block form of a radio receiver circuit employing our invention;

Fig. 2 is a perspective View of one form of a tone control for use in Fig. l;

Fig. 3 is a diagram of the low-pass iilter illustrated in block form in Fig. l;

Fig. 4 is a diagram of the high-pass nlter illustrated in block form in Fig. 1;

Fig. 5 is a schematic diagram in block form of a radio receiver circuit employing a modiiication of our invention.

In Fig. 1, the invention is shown as applied to a, combined radio and phonograph. The radio and phonograph inputs may be conducted to terminals lll and Il of a switch i2 whereby either input may be selectively connected to the sound reproducing system.

A volume control i3 which preferably, out not necessarily, is of the acoustically compensated type is operatively connected between the switch l2 and the rst audio frequency amplifier ifi. The output of ampliiier hl is conducted to two circuits connected in parallel. The first circuit consists of a low-pass filter l5, volume control I6, low frequency ampliiier il and a speaker it. The second circuit includes a high-pass iilter lil, Volume control Z, high frequency audio amplilier 2|, and a speaker 22. Filters i5 and i9 are designed, by way of example, to divide the high and low frequencies into separate channels, with a cross-over point at approximately 250 cycles per second.

The novel tone control mechanism consists of a control which may be a potentiometer, in each circuit operatively connecting the output of the filter to the audio amplifier of the circuit in which the potentiometer islocated. Each potentiometer is operatively connected to the grid of the amplier in its circuit. More specifically, potentiometer iii operatively connects the output of iilter l5 to the control grid of amplifier li, while potentiometer 20 operatively connects the output of iilter I9 to the control grid of audio ampliiier 2l. Potentiometers i6 and 20 are further connected in electrical opposition and are mechanically interconnected so that variation of the power input to one audio amplifier is simultaneously accompanied by a correspondingly opposite variation of the power input to the other audio amplifier. In this manner, a decrease in power input to one audio amplifier will be accompanied by a correspondingly increased power input to the other audio amplifier, thereby maintaining the total volume outputl of the two amplifiers substantially constant.

The specific mechanical connection for the two potentiometers is shown in Fig. 2. Potentiometers I6 and 2li are mounted in tandem with the resistor body surrounding the shaft 20a. The potentiometers may be of the wire wound type as shown, or they'may be of the well known carbon type.

The potentiometers are connected in the circuits in electrical opposition so that a clockwise rotation of shaft 20a will move slidable fingers Zlib and Zilc in the same direction but with the opposite electrical effect. Otherwise stated, clockwise rotation of shaft 2da will result in an increase in the input to the high frequency arnplier 2| of Fig. 1, and a corresponding decrease in the input to low frequency amplifier H of that figure. Thus, by clockwise rotation of shaft 20a the high frequency gain is accentuated while the low frequency gain is correspondingly suppressed by a similar amount. Counterclockwise rotation of shaft-I 20a will result in a suppression of the high frequency gain and a corresponding accentuation of the low frequency gain so that the total volume output of the two speakers will remain substantially constant.

In Figs. 3 and 4 there is shown thev ohmic values of the resistors and the values ofv capacitances of the -condensers of the low and high4 pass lters. These parameters have been found suitable in one illustrative practical embodiment of the invention. These filters are illustrated as being of the resistance-capacitance type, and with the values indicated have a cross-over point of approximately 250 cycles per second. It will readily be understood, however, that the cross-over lpoint is purely arbitrary and that the nlters may be inductance-capacitance filtersl rather than resistance--capacitance filters as shown. Filters of the resistance-capacitance type are preferred because they provide a relatively sharp cut-off at low cost. The high insertion lossinherent therein is overcome by providing the-first amplifier stage I4. Fig. 3 illustrates the arrangement of the low pass filter and Fig. 4 illustrates the arrangement of the high-pass filter.

Referring to Fig. 3, the low-pass filter I5 is made up of three filter stages, the rst and second stages consisting of a seriesl combination of a resistance and a capacitance shunted' by another capacitance, and the third. stageconsisting of two resistances in series shunted by a capacitance. Stage one consists of a series combination of resistance 23 and 4capacitance 24 shunted by capacitance 25,. grounded at 26. Stage two which is operatively coupled' tov4 stage one across capacitance 25 and is composed of resistance 27, capacitance 28 and capacitance 29 grounded at 30. Stage 3 is made up' of rsistances 3| and 32 grounded at 33, shunted by a capacitance 34which in turn is grounded at 35. A potentiometer 36 is provided for the output of the filter.

In Fig. 4, the high-pass filter is shown consisting of three. stages, the first and second stages P each consisting of a capacitance and a resistance in series shunted by means of' a combination of a capacitance and resistance in series, and also by means of still another resistance in parallel with that combination. The third' stage constitutes a single capacitance and resistance i'n series. Stage one consists of capacitance 3'! and resistances 3B and 39 grounded' at 4'0. Resistance 39 is shunted by capacitance `M and resistance 42 which in turn is grounded at 4-3. Stage two which is operatively coupled to stage one across resistance 39, is composed of capacitance 44 and resistances 45 and 46 grounded at 4T. Resistance 46 is shunted by meansl of capacitance 48 and resistance 49 grounded at 50. Both of the resistance-capacitance shunts for stages one and two are connected in parallel withv the resistance shunts of the respective stages. Stage' 3, which is operatively coupled to stage two across resistance 4B, is made up of capacitance 5I and resistance 52 grounded at 53. Apotentiometer 54' is provided for the output of the filter. With the values of the resistances and capacitances given, the low-pass filter is designed' to" pass audio frequencies of a value less than and' upto 250y cycles per second, which the high-pass filter is designed to pass audio frequencies of a value greater than 250 cycles per second. In this manner, separate channels of high and low audio frequencies are obtained. It will readily be understood, however, that the filters may be arranged to pass audio frequencies of a diiferent limited frequency than that indicated. The output potentiometers' 36 and 54 are combined into a dual unit, with the potentiometers connected in electrical opposition so that a clockwise rotation of a single shaft upon which they are mounted will increase the high frequency gain and simultaneously decrease the low frequency gain or vice versa, as explained in connection with Figs. 1 and 2.

From the foregoing, it will be understood that by rotation of a single control, the upper and lower registers may be simultaneously accentuated or decreased without changing the general volume level of the output. The general volume level may be regulated by volume control I3, which, as stated, may be a potentiometer. The adjustment of the base register or treble register may thus be made in a single operation.

A modification of the circuit shown in Fig. 1 is illustrated in Fig. 5. In this embodiment of the invention, a capacitor 55 is connected in series with high-frequency potentiometer 20 and ground in order to control the high frequency response in a different manner than that heretofore described. In this embodiment of the invention counter-clockwise rotation of control 2D will not reduce all frequencies by the sameamount, but rather results in a disproportionate reduction of the high and low frequencies. More specifically stated, counter-clockwise rotation of control 20 reduces the eXtreme high frequencies most, while at the same time resulting in a smaller attenuation of the lower frequencies.

It will be observed that We have provided a system including two independent circuits and speakers, together with mechanically interconnected gain and/or fidelity controls and thereby provided a means whereby the volume of one register may be either accentuated or suppressed and the volume of another register may be simultaneously suppressed or accentuated in opposition to the variation of the volume in the first register so that the total volume output remains substantially constant in spite of the change in tone quality.

While this invention has been shown and described in two particular embodiments thereof, it will be understood that various changes and modifications may be made therein coming Within the scope of the appended claims.

Having thus described our invention, we claim:

l. The method of tone control for an electronic sound reproducing system which consists of dividing the energy input to the system into a pair of channels, ltering the energy in said channels to suppress frequencies above a predetermined value in one of said channels and to suppress frequencies below a predetermined value in the other of said channels, increasing the gain in one of Said channels, and simultaneously decreasing the gain in the other of said channels by a corresponding amount to thereby maintain the total output substantially constant.

2. Apparatus for tone control of an electronic sound reproducing system of the dual-speaker, dual-channel type including a pair of energy transmitting circuits each connected to receive a portion of the input energy of the system, filtering means in each `circuit adapted to suppress predetermined portions of the audio frequency band, control means associated with one of said circuits for varying the gain therein, control means associated with the other of said circuits and connected in electrical opposition to said rst mentioned control means for varying the gain in said circuit, means for simultaneously actuating said control means, and independent transducer means for receiving the output of each of said circuits.

3. Apparatus for tone control of anelectronic sound reproducing system including a pair of energy transmitting circuits each connected to receive a part of the input energy of said system, filtering means in each circuit adapted to suppress certain portions of the audio frequency band, a separate gain control unit associated with each circuit, a mechanical connection between said gain controls for simultaneously actuating said controls, said gain control units being so phased and said mechanical connection being so arranged that one of said portions is accentuated when the other of said portions is attenuated, whereby the general volume level is maintained constant, and transducer` means for receiving the output energy of each of said circuits.

4. Apparatus for tone control of an electronic sound reproducing system of the dual-speaker, dual-channel type including a pair of energy transmitting circuits each connected to receive a part of the input energy of said system, ltering means in each circuit adapted to accept certain diierent portions of the audio frequency band, a gain control associated with one of said circuits, a gain control associated with the other of said circuits connected in electrical opposition to said iirst-mentioned gain control, means for simultaneously actuating said gain controls, and independent transducer means for receiving the output of each of said circuits.

5. Apparatus for tone control of an electronic sound reproducing system including a pair of energy transmitting circuits each connected to receive a part of the input energy of said system, filtering means in each circuit adapted to suppress certain portions of the audio frequency band, an output potentiometer associated with one of said circuits, an output potentiometer coupled to the other of said circuits, means for simultaneously dilerentially actuating said potentiometers, and independent acoustic reproducing means for receiving the output energy of each of said circuits.

JOHN DRYSDALE REID. PAUL F. G. HOLST.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Roberts Sept. 16, 1941 

